Prominent Islamist leader Abdel Krim - nicknamed "Kojak" - is reported to have been killed in the strikes.

A 600-strong multi-national West African force, authorised by the UN Security Council to help the Mali government reclaim control of the north of the country, is also on its way to the capital Bamako. It will be commanded by General Shehu Abdulkadir of Nigeria.

In addition, Burkina Faso, Niger, Senegal and Togo have all pledged around 500 troops this weekend, while Benin has said it will send 300 soldiers.

French military strikes on the country have already claimed the lives of at least 100 rebels in a fight over the strategic town of Konna.

Eleven Malian soldiers are reported to have been killed and a further 60 wounded in the recent fighting.

He said France "has to take all necessary precautions" in the face of a terrorist threat, including "surveillance of our public buildings and our transport network".

A Downing Street spokesman said last night: "The Prime Minister spoke to President Hollande this evening to discuss the deteriorating situation in Mali and how the UK can support French military assistance provided to the Malian government to contain rebel and extremist groups in the north of the country.

"The Prime Minister has agreed that the UK will provide logistical military assistance to help transport foreign troops and equipment quickly to Mali.

"We will not be deploying any British personnel in a combat role.

"Both leaders agreed that the situation in Mali poses a real threat to international security given terrorist activity there.

"They discussed the need to work with the Malian government, regional neighbours and international partners to prevent a new terrorist haven developing on Europe's doorstep and to reinvigorate the UN led political process once the rebel advance has been halted.

"The National Security Council, which was already due to meet on Tuesday, will now consider the situation in Mali and discuss what needs to be done to secure a lasting political settlement in Mali."

One French pilot has died in the military action after hundreds of French soldiers were deployed in the country.

Mr Hollande took action in Mali at the request of interim President Dioncounda Traore, who has declared a state of emergency.

The Malian army has said it was attacking the "last pockets of resistance" by insurgents in Konna after they recaptured it with the help of the French.

Mr Hollande said the "terrorist groups, drug traffickers and extremists" in northern Mali "show a brutality that threatens us all." He vowed that the operation would last "as long as necessary".

The West African regional bloc ECOWAS has now authorised the immediate deployment of troops to Mali.

The bloc's commission president, Kadre Desire Ouedraogo, said it made the decision "in light of the urgency of the situation".

For the past nine months, the Islamic militants have controlled a large swathe of northern Mali, a lawless desert region where kidnapping has flourished.

Mr Hollande said the operation was aimed in part at protecting 6,000 French citizens in Mali, including seven who are being held captive.

UN Secretary-General Ban Ki-moon said Senegal and Nigeria also responded to an appeal from Mali's president for help to counter the militants.

Late last year, the 15 nations in West Africa, including Mali, agreed on a proposal for the military to take back the north, and sought backing from the UN.

The Security Council authorised the intervention but imposed certain conditions, including the training of Mali's military, which has been accused of serious human rights abuses since a military coup last year sent the nation into disarray.

Al Qaeda's affiliate in Africa has been a shadowy presence for years in the forests and deserts of poverty-stricken Mali.

Most Malians adhere to a moderate form of Islam, but in recent months the terrorist group and its allies have taken advantage of political instability, taking territory they use to stock weapons and train forces.

The Islamists have insisted they want to impose Sharia only in northern Mali, though there long have been fears they could push further south.